In combat areas, such as Vietnam, it has proven extremely difficult to distinguish between friendly and unfriendly native forces. Individual screening and interrogation is not always possible or feasible and, frequently, it simply compounds the confusion. Substantial efforts have been devoted toward providing a more reliable means of identification, the instant proposal being to deposit fluorescent materials on the perimeter of a particular zone. Infiltrators pick up the fluorescent material permitting identification to be made.
Such a concept is entirely feasible, but there have been difficulties both in providing suitable marker materials and in developing adequate means for producing and viewing the fluorescence. While there are a number of devices capable of both illuminating and viewing fluorescence at close range, such a procedure requires personal and individual contact with the suspect and therefore does not permit a broad scanning of an area such as would enable a suspect to be picked out of a relatively large group. One complication arising particularly during daylight hours is that the fluorescence is relatively dim and difficult to detect particularly when sunlight or other light sources produce interfering backgrounds.
Also, from a practical point of view, apparatus suitable for such uses should be easily portable and also relatively inexpensive if it is to be used extensively in the field. Expensive, heavy equipment which conceivably might generate sufficient power to accomplish the present purposes are not acceptable.